1. Field of the Invention
This invention relates to methods and systems for fabricating electronic circuits, and particularly to apparatus and methods incorporating shadow masks and shadow mask cleaning in the manufacture of integrated circuits.
2. Description of Related Art
Large area active electronic devices are widely used in flat panel displays and related technologies. For example, active matrix backplanes are used in flat panel displays for routing signals to pixels of the display in order to produce viewable pictures. Active matrix backplanes, as well as other large area electronic circuits, are multilayer devices presently manufactured using photolithography, a pattern definition technique that uses electromagnetic radiation, such as ultraviolet radiation, to expose a layer of a photoresist material deposited on the surface of a substrate. Exemplary photolithographic processing steps to produce a layer of a multilayer active matrix backplane on a substrate include: coat with photoresist, pre-bake, soak, bake, align, expose, develop, rinse, bake, deposit a layer, lift off the photoresist, scrub, rinse, and dry.
Photolithography-based manufacturing methods thus include a wide variety of both additive (material deposition) steps and subtractive (material removal) steps, requiring large, complex and expensive fabrication facilities that incorporate many disparate manufacturing technologies. Furthermore, many photolithographic manufacturing steps must be carried out in clean room environments, further driving the manufacturing complexity and costs high.
Alternatively, a vapor deposition shadow mask process is well-known and has been used for years in microelectronics manufacturing. The vapor deposition shadow mask process is a significantly less costly and less complex manufacturing process, compared with photolithography-based manufacturing. The vapor deposition shadow mask process can be used to form one or more electronic devices on a substrate using additive processes only. This is done by sequentially depositing patterns of materials including conductors, semiconductors and insulators, through complementary patterns of apertures in shadow masks positioned between one or more material deposition sources and the substrate.
One challenge in implementing all-additive process steps for the volume manufacturing of electronic circuits is that as a shadow mask is used repetitively for patterning a material onto a substrate, the mask also accumulates the material on its surface and in its pattern of apertures, changing the dimensions of the apertures and thereby degrading mask performance for future depositions through that mask onto a substrate. Frequent replacement of a shadow mask, especially a large area mask, generally is neither practical nor cost-effective for a volume manufacturing process. Some degraded shadow masks may be cleaned to remove deposited material from the mask, but shadow mask cleaning is generally considered incompatible with high volume production of electronic devices because most mask cleaning methods are very slow or labor intensive or would require that the mask be removed from a production line and brought to a separate environment for cleaning.
Accordingly, a need exists in this art for equipment and methods to rapidly and cost-effectively clean shadow masks in a volume manufacturing setting. In addition, a need exists for apparatus and methods for rapidly replacing a used shadow mask for a fresh shadow mask in a manufacturing line.